Outdoor heat exchanger in air conditioning heat pump (ACHP) system would frost quickly under a low-temperature but high-humidity surroundings. System performance and efficiency would significantly decrease without a rapid and appropriate defrosting strategy. In this work, a quick response reverse cycle defrosting strategy for an ACHP system in electric vehicles is presented, and its effectiveness is validated experimentally. Frosting experiments were conducted to capture the typical heat transfer parameters and frosting behaviors, and then the frost coverage ratio was obtained with threshold division method. An uneven frosting process were observed on the surface of the microchannel outdoor heat exchanger due to uneven dryness distribution. Then a certain frost coverage ratio was obtained as the reverse start criteria, and a series of defrosting experiment were conducted in validation of the reserve defrosting strategy. Results show that the frost coverage ratio of 0.56, or 2 °C deterioration of indoor outlet air temperature can be chosen as the reverse start criterion value with the current reverse cycle defrosting strategy for vehicular ACHP system. Frost can be almost removed completely within 40s with the proposed reverse defrosting strategy under the condition of ambient temperature 0–5 °C and relative humidity 80–85%.

空调热泵（ACHP）系统中的室外换热器在低温高湿环境下会迅速结霜。如果没有快速和适当的除霜策略，系统性能和效率将显着下降。在这项工作中，提出了一种用于电动汽车 ACHP 系统的快速响应逆循环除霜策略，并通过实验验证了其有效性。通过结霜实验捕捉典型的传热参数和结霜行为，然后用阈值划分法获得霜冻覆盖率。由于干燥度分布不均，在微通道室外换热器表面观察到不均匀的结霜过程。然后得到一定的霜冻覆盖率作为反向启动标准，并进行了一系列的除霜实验，验证了备用除霜策略。结果表明，当前车载空调冷气系统逆循环除霜策略可以选择0.56的霜冻覆盖率，即室内出风温度恶化2℃作为逆向启动判据。在环境温度0～5℃、相对湿度80～85%的条件下，采用所提出的逆向除霜策略，40s内几乎可以完全除霜。